Microbes in insect gut significantly influence host physiology. While Lepidoptera is a diverse insect order, the relationship between microbial symbiosis and host development remains elusive, especially concerning role of gut-colonizing bacteria in metamorphosis. We investigated the gut microbial diversity in Galleria mellonella throughout its life cycle using 16S rRNA amplicon sequencing. Our findings revealed a predominance of Enterococcus spp. in larvae and Enterobacter spp. in pupae. Remarkably, removing Enterococcus spp. hastened the larval-to-pupal transition. Transcriptome analysis showed an upregulation of immune response genes in pupae and hormone genes in larvae. Notably, the production of antimicrobial peptides in the host gut varied with developmental stages. Some of these peptides suppressed the growth of Enterococcus innesii, a dominant gut bacterium in G. mellonella larvae. This research underscores the pivotal role of gut microbiota shifts in metamorphosis, driven by the secretion of antimicrobial peptides in the G. mellonella digestive system.

Agrobacterium tumefaciens causes crown gall disease by transferring its DNA into host plants. Although Agrobacterium can be popularly used for genetic engineering, above-ground insect infestation in Agrobacterium gall formation has not been investigated. Nicotiana benthamiana leaves were exposed to a sucking insect whitefly infestation and a chemical trigger, benzothiadiazole (BTH), for 7 days, and these exposed plants were inoculated with Agrobacterium. We evaluated how whitefly infestation manipulated gall disease by Agrobacterium in planta and in vitro. Insect whitefly infested plants exhibited at least a 2-fold reduction in gall formation on both stem and crown root. Silencing isochorismate synthase 1 (ICS1), required for salicylic acid synthesis, compromised gall formation, indicating an involvement of salicylic acid in whitefly-derived plant defense against Agrobacterium. Endogenous salicylic acid content was augmented in whitefly-infested plants by Agrobacterium inoculation. However, infestation with whitefly did not alter Agrobacterium root colonization but reduced expression levels of genes involved in Agrobacterium virulence and transformation efficiency. Above-ground whitefly infestation therefore elicits systemic responses throughout the plant. Our findings provide new insights into insect-mediated leaf-root intra-communication and a framework to understand a general principle in multitrophic interactions in nature.

We analyzed the viable population changes of Paenibacillus polymyxa E681, a plant growth-promoting rhizobacterium, on seeds and roots after bioformulation at varying time intervals during the storage. The viable population of E681 on tested crop seeds sustained log 4-5 cfu/seed after 300 days of seed treatment. The ability of root colonization and inhibition of fungal mycellial growth was not influenced even after 300 days of seed treatment. The seed-soaking treatment returned better results than powder formulation, in increasing the initial population of E681 on plant roots. Collectively, it was found that E681 is a durable and stable biological control agent for application to crop seeds.

Plants have evolved general and specific defense mechanisms to protect themselves from diverse enemies, including herbivores and pathogens. To maintain fitness in the presence of enemies, plant defense mechanisms are aimed at inducing systemic resistance: in response to the attack of pathogens or herbivores, plants initiate extensive changes in gene expression to activate “systemic acquired resistance” against pathogens and “indirect defense” against herbivores. Recent work revealed that leaf infestation by whiteflies, stimulated systemic defenses against both an airborne pathogen and a soil-borne pathogen, which was confirmed by the detection of the systemic expression of pathogenesis-related genes in response to salicylic acid and jasmonic acid-signaling pathway activation. Further investigation revealed that plants use self protection mechanisms against subsequent herbivore attacks by recruiting beneficial microorganisms called plant growthpromoting rhizobacteria/fungi, which are capable of reducing whitefly populations. Our results provide new evidence that plant-mediated aboveground to belowground communication and vice versa are more common than expected.